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Old 29th October 2010, 12:40 AM   #1
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Default Preamp problem

Hello folks, I have a quick question that I'm hoping someone may be able to help me with. i have an old (1968) Sony TA 2000 preamp.. it has been working fine up until a few nights ago... if you turn the unit on it runs perfectly for approx 5 mins and then a load cracking sound starts from the left channel.. i have my thoughts that it could be a bad transistor but am not sure. i am not an electronics wiz but have dabbled in mods on other equipment with no problems.. I'm driving an Electrocompaniet aw 100 power amp.. the Electro preamp went bad on me a while back and knowone could find out what went wrong with that...id like to try and fix this Sony as it is a nice little piece and i feel a bit of a collectors item.. I am working on saving up for a new preamp but in the meantime this would do fine.. any thoughts on this problem would be greatly appreciated.. Thank you on advance...... Jaime
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Old 29th October 2010, 03:34 AM   #2
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A transistor or capacitor may be failing. Hard to guess with such minimal information.
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Old 29th October 2010, 05:20 PM   #3
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Get a can of MG "Super Cold 22" spray. Open the box and turn it on (a heat lamp could help the process). After the amp acts up freeze the individual components till you find the culprit.
E
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Old 29th October 2010, 06:12 PM   #4
LAJ is offline LAJ  United States
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Default Try this.

Is it shock sensitive? Try tapping on it. Does it make the noise? Might be just a loose connection. That loud cracking is an erratic DC fluctuation. My guess is a cap since it is very old (1968). Keep your volume down when it does this or you'll need new speakers too.
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Old 29th October 2010, 06:48 PM   #5
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Most probably, the problem is a coupling capacitor which is failing.
It's a 40+ year old piece of equipment.
It would probably be wise to replace all electrolytic capacitors.
Good luck.
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Old 30th October 2010, 12:42 AM   #6
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Quote:
Originally Posted by mickeymoose View Post
Get a can of MG "Super Cold 22" spray. Open the box and turn it on (a heat lamp could help the process). After the amp acts up freeze the individual components till you find the culprit.
E
INTERESTING CONCEPT. IS THIS R-22 REFRIGERANT? I HAVE ABOUT 20 LBS OF IT IN THE GARAGE.. IT WOULD CERTAINLY COOL OFF A COMPONENT IF SPRAYED ON IT...THANK YOU

Last edited by jaimeblackwell; 30th October 2010 at 12:57 AM.
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Old 30th October 2010, 12:49 AM   #7
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Quote:
Originally Posted by LAJ View Post
Is it shock sensitive? Try tapping on it. Does it make the noise? Might be just a loose connection. That loud cracking is an erratic DC fluctuation. My guess is a cap since it is very old (1968). Keep your volume down when it does this or you'll need new speakers too.
it is not shock sensitive if you bump it but it was shock sensitive as far as a low voltage tingle right be for it started acting up. it only caused a shock if i touched the preamp and amp at the same time.. in leaning toward a grounded component..
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Old 30th October 2010, 12:56 AM   #8
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Quote:
Originally Posted by Frank Berry View Post
Most probably, the problem is a coupling capacitor which is failing.
It's a 40+ year old piece of equipment.
It would probably be wise to replace all electrolytic capacitors.
Good luck.
Thank You for you comment Frank, i plan to pull the two 1000 uf caps on the power supply tonight.. i have two kicking around and figured id try them out.. i will test the existing caps with my meter but most likely change them anyways...
i guess you would call these the output caps i will have to check the schematic to see if i can locate the coupling caps.. if so is it a wise choice to use polypropylene caps in there place.. if so it should improve the sonics greatly... what are your thoughts on this.. thank you?
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Old 30th October 2010, 12:47 PM   #9
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Do it right and replace them all, we're not talking about any serious money. It's 40 yrs old. And clean all the pots and switches.
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Old 30th October 2010, 07:27 PM   #10
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you are right Bill. i did clean all the pots and switches already. and last night i did replace the two 50 uf caps on the power supply board..i had those caps in my box of stuff so i figured id start there... it was working fine for 2 hours and then the crackling came back.. i was disappointed to say the least. but at the same time i had lost about 30% of gain after the repair. so i knew i wasnt done yet... i has got to pick up the rest of the caps and then i will sit down and start the replacement process. poly propylene caps are out of the question due to the overall size but i will see if i can tweek it a bit as i go..
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